Electrical plug



prl 16, 1935. J. M. G. FULLMAN ELECTRICAL PLUG Filed Feb. 25, 1955 dames M. G. Fill/man Millar ATTORN EYS Patented Apr. 16, 1935 UNITED STATES PATENT OFFICE 1,998,129 ELECTRICAL PLUG` Application February 25, 1933, Serial No. 658,499

9 Claims.` (Cl. 173-356) This invention relates to y screw plugs for electric sockets.A In its broader aspects, the invention is applicable to screwplugs generally, but it is particularly suited to fuse plugs or dummy fuse plugsand hence will be specifically disclosed in that connection. 1

In many instances it is desired to insert into an electric socket a screw plug which may be readily removed by an authorized person but which is difficult to removerby an unauthorized person. One example is fuse plugs used to protectA circuits from overload.A It is a matter of common occurrence that when afuse plug blows out a consumer or uninformed personremoves the plug andrestores thecircuit by placing beneath the burnt out plug a coin, vtinfoil, or the like, thus leaving the circuit without protection. If the plug were not removable by the consumer, an authorized person would have to be called, and he would see that the circuit was in proper condition to again have power applied yto it and would then install a new fuse of the proper rating.

Anotherinstance in which it is desired to prevent the removal of plugs is where dummy plugs are put into thefuse socket to cut oi the supply of current to a particular consumer, sub-tenant, or the like. Such cut-ois can, Vof course, be made by means of lock switches, but these are relatively expensive and in practice the circuit may not be already equipped with such a device whereas the circuit is always equipped with a fuse socket into which a dummy plug can be inserted. 1 l

A general object of the invention isto provide an improved screw plug for electric sockets which can be readily inserted into the socket in the conventional manner and can be readily removed by an authorized person, but which is difficult or impossible of removal Aby an unauthorized person.

Another object of the invention is to provide a rugged inexpensive plugy capable of insertion into an electric socket in the conventional manner and incapable of removal without a special tool of a type not likelytoY be inthe hands of an unauthorized person. y

A more specific objectof the invention is to provide a' dummy fuse plug having an appearance which does not advise the uninitiated that it is a dummy and which can only be removed from the socket by special means which are normally out of View of an observer and are 'not likely to be discovered by the uninitiated'.

The present invention is in some respects an improvement upon the plug disclosed in the patent to Schmidt 1,841,638, January 19, 1932.

Fig. I is a cross sectional view showing a preferred embodiment of the invention in place in a conventional fuse socket. f

Fig. II is an exploded view showing the vari ous component parts of the plug.

Fig. III is a perspective View showing a modied anging of the pivot pin.

Fig. IV is a perspective View showing a special tool for removing the plug from the socket.

In Fig. I there is shown avconventional fuse socket having a center electric contact I and a screw threaded shell contact 2. Circuit connection to the socket contacts is adapted to be made through terminal 3 and lead 4 which may be so arranged that it is difficult to wire around the fuse. The supporting structure for the conducting parts of the socket is usually made of some such material as porcelain and the shell contact 2 of the socket is usually embraced by an annular insulating wall 5 which substantially encloses it.

The dummy plug has a Anose 8 and an operating head S each of which are preferably molded from a suitable insulating material such as fiber, porcelain, a phenol condensation product, or the like. The nose 8 has a screw thread I0 adapted to cooperate with the shell 2 of the socket; and the operating head 9 is superimposed upon the nose 8 and swiveled thereto through a metal pivot pin II` The vpivot'pin I I is provided with a square head I2, which iits in a square aperture I3 in the nose 8, and with a shank I4 which extends upwardly through a central bore in the head 9 and into the recess I5 of the head 9. Interposed between the nose 8 and the operating head 9 is a ratchet disc I6 of spring metal, having depending iingers II which engage in slots I8 in the top of the nose 8. The ratchet disc I6 has spring jaws I9 which cooperate with ratchet teeth 20 molded on the bottom of the head 9 to establish a one-way rotative driving connection between the head 9 and the nose 8.

In assembly, the pivot pin II is put in place in the nose 8; the ratchet disc I6 and the spacing washer 22 are applied over the pin; the head 9 and a washer 23 are then applied; and the tip of the pivot shank is then treated in some suitable way to secure the parts together without such clamping as would destroy the swivel action. In Figs. I and II the pivot pin I I is shown provided with a circular bore, and the shank end of the pin is flanged outwardly at 24 by a stamping, pressing, or spinning operation to secure the head; a pivot pin having a head embraced by the material of said nose and a shank extending to the recess of said operating head and making free pivotal connection to the operating head, the shank end of the pin having a circular bore to receive a reamer-like tool to rotate the pin for removing the nose from the socket, the extremity of the shank being ilanged outwardly to secure said nose and operating head together;

and a frangible closure covering the recess in the 10 operating head.

JAMES M. G. FULLMAN. 

